This invention relates to a temperature sensing circuit using insulated gate field effect devices for sensing temperature.
In particular, this invention relates to a temperature sensing circuit comprising a first insulated gate field effect device, a second insulated gate field effect device, means for operating the first insulated gate field effect device in its subthreshold region so that the voltage across the first insulated gate field effect device varies with temperature, and means for comparing the voltages across the first and second insulated gate field effect devices.
Such temperature sensing circuits are described in, for example, GB-A-2096771 and a paper entitled "Integrated MOS temperature sensor" by R. C. Jaeger and D. V. Kerns published in the Conference Proceedings of the 1980 IEEE Region 3 Conference and Exhibit Apr. 13, 14, 15, 16, 1980 Nashville, Tenn.
In each of these prior documents, the first and second insulated gate field effect devices are each formed by an insulated gate field effect transistor (IGFET). The two IGFETs are arranged to be operated in their subthreshold region where the drain current Id varies logarithmically with the gate-to-source voltage Vgs in a manner such that the slope of the Id versus Vgs curve is constant over many decades and directly proportional to temperature. The two IGFETs are arranged to have different drain currents by, for example, appropriately scaling the channel width and length geometry of the IGFETs and/or by appropriately scaling load resistors connected in series with the IGFETs. The difference in the gate-source voltage .increment.Vgs of the two IGFETs may thus be used as a measure of absolute temperature.